Injection-molding machines require unambiguously reproducible production conditions for a smooth, fully automated production sequence. In the case of the liquid silicone technology (LSR=liquid silicone rubber) known since approximately 1980, the low-viscosity silicone rubber components are admixed with one another using suitable dosing and mixing units and vulcanized in the injection-molding method at elevated temperature in the mold cavity. This technology allows high cycle rates due to the short cross-linking duration. However, this technology has the disadvantage that there is a high power demand for the temperature increase for the vulcanization.
A further disadvantage results from the circumstance that many thermoplastic materials tend to deform at elevated temperature because of their nature and due to this circumstance, heretofore connecting a hard, thermoplastic plastic with a soft, permanently elastic silicone plastic by way of injection-molding methods was not possible without quality losses. Due to the development of light-activatable LSR materials, for which a separate temperature supply is not necessary for the cross-linking thereof in the mold cavity, novel possibilities have now resulted for solving the previous problems in the injection-molding processing of LSR materials.
Light-activatable polymer compositions, in particular silicone compositions, have been known for some years. Thus, for example, DE 10 2008 000 156 A1 describes a hydrosilylation reaction activatable by radiation, in which silicone products which can be cross-linked by radiation using UV light or using visible light are produced. Furthermore, EP 1 817 372 describes a siloxane composition activatable by irradiation with light, which allows the production of thick-walled molded articles containing fillers and/or pigments. Further silicone compositions which can be cross-linked by irradiation with visible light or with UV rays are known from U.S. Pat. No. 4,699,802, EP 0 146 307, U.S. Pat. No. 6,376,569 and WO 92/10544.
Furthermore, devices having transparent windows for irradiation of light-activatable polymers are known from the prior art. Thus, for example, U.S. Pat. No. 5,401,155 describes a metal mold having a light-transmissive window, which is arranged perpendicularly to a light source. A two-part mold for the production of lenticular plastic products from light-curing polymer material, in which one mold half consists of light-transmissive material, is known from U.S. Pat. No. 6,627,124. WO 2011/101269 describes a mold cavity made of two transparent walls having UV lamps arranged behind each of them.
Activating light-activatable silicone rubber compositions using UV light immediately before they are injected into the mold cavity is also known, wherein the light dose and the irradiation time, and also the remaining transport distance and the transport speed have to be adapted in such a manner that the curing only occurs in the mold cavity, but not already before the silicone rubber composition enters this mold cavity.
All of these methods, however, have the disadvantage that the irradiated plastic composition is carried out without any monitoring of the temperature control. However, the reaction profile of photoactivated cross-linking processes is always dependent on the temperature of the starting material at the point in time of the photoactivation or the beginning of the cross-linking, respectively, wherein the temperature dependence of the cross-linking speed is dependent on the specific composition of the starting material and its additives, of course.